Fix: Migrations are not Postgres compatible

With length field for "age" column, the resultant SQL is 

CREATE TABLE "pet" ("id" varchar(255) NOT NULL, "name" varchar(255) NOT NULL, "age" int(11) NOT NULL, "user_id" varchar(255), CONSTRAINT "PK_b1ac2e88e89b9480e0c5b53fa60" PRIMARY KEY ("id"))

This will fail in postgres due to [int(11) being non standard](https://www.postgresql.org/message-id/18103.1013471731%40sss.pgh.pa.us)

By removing "length" property, the resultant sql uses 'age int NOT NULL', which works in postgres and mysql both ( I have also verified it for oracle)

Author: prog-rajkamal

src/database/migrations/1512663524808-CreatePetTable.ts

@@ -21,7 +21,6 @@ export class CreatePetTable1512663524808 implements MigrationInterface {
                 }, {
                     name: 'age',
                     type: 'int',
-                    length: '11',
                     isPrimary: false,
                     isNullable: false,
                 }, {